60 FLATWORMS AND MESOZOA, ETC. 



Passing now to the Termatoda, we have only space for a very 

 short extract from the Life-history of the Liver Fluke, Distoi7iuin 

 hepaticum^ which produces the disastrous disease, liver rot; it has 

 a distribution as wide as that of a water-snail, LimncBa truficatula^ 

 the connexion between the two being, as Thomas and Leukart 

 discovered, that this snail is the intermediate host in which the 

 larval, sporcyst, and redia stages are passed through, and a vast 

 number of immature flukes (Cercarice) are developed. These 

 leave the snail and encyst upon grass, where they are eaten by the 

 sheep. . . . Meadows of a clayey soil, liable to be flooded 

 (as in certain parts of Oxfordshire), are the places where this 

 LimncBa occurs most abundantly, and these are, consequently, the 

 most dangerous feeding-grounds for sheep. 



Although we find every page of the book exceedingly inte- 

 resting, we are compelled to pass on to the last section, Polyzoa, a 

 section which we are sure will delight every microscopist, as it 

 deals with animals which are scarcely known except to those who 

 are professed naturalists. 



" There are but few Polyzoa which have earned the dis- 

 tinction of possessing a popular name, and most of such names as 

 do exist cannot be found outside of Treatises on Natural History. 

 It is true that many of the members of this group have been 

 vaguely called "Zoophytes"; but this term implies no more than 



EXPLANATION OF PLATE VII. (see opposite page). 



Diagrammatic view of the structure of Leptoplana tremellaris 

 as a type of the Polycladida. The body is cut across the middle to 

 show the relative position of the organs in transverse section. In the 

 posterior half the alimentary canal has been bi-sected and removed 

 from the left side to exhibit the deeply-placed nervous sheath (n.n.), 

 and the male reproductive organs. 



67-., Brain; dp., Diaphragm; e., cerebral group of eyes; e.t., 

 Tentacular eye-group; gr., marinal groove; gm., True mouth; l.g., 

 Lateral gut-branch; l.n., Longitudinal nerve stem; m. , External 

 mouth; m.g., m.g.', Main gut, whole and bi-sected; n., Sensory 

 nerve supplying the eyes ; n.n., Nervous network lying on the ventral 

 musculature; ns., Lateral nerve; od. , Oviduct; ov., Ovary; |)e., 

 Penis (in section) ; ph., Pharynx ; pr., prostrate, or " granule gland" ; 

 sc, Sucker; s.g., Shell-gland; te., Testes; up>., Anterior unpaired 

 gut-branch ; ut., Uterus ; va.. Vagina (in section) ; v.d., Vas 

 deferens ; v.e., Vasa efferentia ; c? Male genital pore ; $ Female 

 pore. 



